1. Field of the Invention
The present invention relates to a method of manufacturing a flash memory device, and more specifically, to a method of manufacturing a flash memory device in which the size of the flash memory device can shrink while improving reliability of the flash memory device through a shallow trench isolation (hereinafter, referred to as ‘STI’) process.
2. Discussion of Related Art
Generally, a flash memory device is a stack gate structure consisting of a floating gate and a control gate. In the floating gate, since the active region must be covered, the overlay margin between the active region and the floating gate is an important factor. As the flash memory device gradually shrinks, however, it is difficult to secure the overlay margin between the active region and the floating gate through an existing STI process and an existing floating gate mask process. It is also difficult to obtain the overlay margin uniformity across the entire wafer.
Further, the flash memory device is formed typically by means of a wet etching process when a trench type isolation film is formed by a STI process. If the wet etching process is performed excessively, moats are generated at the boundary between the trench type isolation film and the active region. This makes a subsequent process difficult. Although an etch target of the wet etching process is properly set in order to solve this problem, it is difficult to obtain a uniform isolation film not having moats across the entire wafer.
As such, there is a limit to the shrinkage of the flash memory device due to securing of the overlay margin between the active region and the floating gate and the moats generated at the boundary between the isolation film and the active region.